This proposal constitutes the extension of a successful pilot project that demonstrated the feasibility of applying fluorescent photobleaching technology to the in vivo measurement of lateral diffusion of components in the outer membrane of gram negative bacteria. It is hoped that such measurements will allow: (a) determination of the mobility, within the membrane, of lipid, protein, and lipopolysaccharide; (b) analysis of the potential control mechanisms of lateral mobility and possible relationships to assembly and function of the outer membrane and peptidoglycan shell; and (c) investigate the relationship between reagents that alter the fluid dynamics of outer membrane and viability of bacteria. Further, it is considered likely that diffusion measurements in bacterial membranes, a system which is readily manipulable by genetic and physiological means, will offer a more unambiguous model for the exploration of causal relationships between the molecular composition and organization of a membrane, its fluid dynamics, and specific function.